People tend to think that the telltale sign of depression is sadness—a pervasive down, dragging feeling that won’t let up, day after day. But depression often manifests itself as something else entirely—like aches and pains or memory lapses.

These “unusual” symptoms are actually quite common. They can mask depression—and delay an important diagnosis—especially in older people. “Sometimes it’s hard to diagnose depression in older adults because they don’t come in and say, ‘I’m depressed.’ They’re more likely to present with physical symptoms that they don’t connect with what they’re feeling…pain, memory problems, poor sleep, a change in appetite,” says Dr. Anne Fabiny, chief of geriatrics at Cambridge Health Alliance and assistant professor of medicine at Harvard Medical School.

She’s even seen people fall more frequently because they’re depressed. The connection might not seem logical, until you consider that depression can make people more inattentive to their surroundings.

Older people in particular—and older men especially—display their depression in unusual ways. “Older men are more likely to present with irritability or grumpiness as a symptom of depression than women,” says Dr. Fabiny. “So the stereotype of the grumpy old man could be a sign of a depressed old man.”

A new report from the Centers for Disease Control and Prevention shows that depression is more common among women (10.7% of adult women) than men (7.7% of adult men). And though depression tends to peak between ages 45 and 64, it can emerge at any time of life.

Older men and women with depression often don’t want to talk about it because their generation still harbors a stigma about mental illness. “Older people still have the idea that, ‘I’m not crazy. I don’t want people to think I’m crazy,'” Dr. M. Cornelia Cremens, assistant professor of psychiatry at Harvard Medical School, told me last year for an article in the Harvard Women’s Health Watch.

Dr. Fabiny says she often doesn’t say the word “depression” when talking to her older patients. Instead, she’ll use terms like “sad” or “blue.”

To diagnose depression, she’ll look for signs other than sadness, including:

trouble sleeping

lack of energy

fatigue

trouble concentrating or remembering

loss of appetite

aches and pains that don’t go away

Because of the stigma, Dr. Fabiny says her older patients are more willing to take medicine to treat their depression than meet with a psychologist or psychiatrist. Yet antidepressants tend to be less effective in older adults, they can take up to three months to start working, and the risk of side effects is greater. “Research has shown that a combination of medication and psychotherapy [talk therapy] is really the most effective,” Dr. Fabiny says.

Any treatment, though, is better than none. Leaving depression to fester and grow can cause repercussions that extend far beyond persistent sadness. “There’s a higher rate of mortality in older adults who are depressed and have untreated depression. And it so profoundly affects quality of life. People suffer—and they can also lose functional capacity,” according to Dr. Fabiny. Depression has even been linked to an increased risk of dementia.

If you have one or more of the symptoms listed above that can’t be traced to an illness or ailment, a frank talk with a trusted doctor about the possibility of depression might be a good step forward.